The present invention relates to detergent tablets, especially those adapted for use in washing.
Although cleaning compositions in tablet form have often been proposed, these have not (with the exception of soap bars for personal washing) gained any substantial success, despite the several advantages of products in a unit dispensing form. One of the reasons for this may be that detergent tablets usually dissolve slower than the constituent powders from which they are made, simply because the constituent powders are forced close together in the tablet, with comparatively little opportunity for water to permeate between them. This gives rise to the problem that slow dissolving tablets cause residues which may for example be visible through the door of the washing machine during the wash cycle, or which stick to the fabrics at the end of the wash cycle, or both. This may be compensated by using low compression forces to keep high porosity and good dissolution profile. However, such tablets are typically softer and have mechanical characteristics such that breakage is likely to occur during production or handling.
DE-A-2 207 633, published on the 30th of August 1973, discloses tablets having three layers, the middle layer being sandwiched between two end layers, the two end layers being made so as to protect the middle layers from mechanical shocks, while allowing tablet dissolution in less than a minute.
However, particularly in certain front loading washing machines, problems of tablet residues appearing visibly at the window of the washing machine have still been encountered. Indeed, in particular for detergent tablets, the dissolution problems are particularly acute, due for example to the tendency of gelling of the surfactant materials, or to low level of water used for environmental reasons, or due to dissolution at low temperature, etc.
The object of the present invention is to provide detergent tablets typically formed by compressing a particulate material, the tablet being suitable for storing, shipping and handling without breakage while dissolving easily and rapidly in wash solution, releasing the active ingredients into the wash solution and completely disintegrating and dispersing in alkaline or surfactant-rich solutions such as the wash liquor.
The object of the invention is achieved by providing a detergent tablet having at least a first and a second layer, whereby the first layer is softer than the second layer, and if said tablet has more than two layers, the tablet is such that a softer layer is situated at an end of the tablet.